How useful are widgets?

I'm brand new to the blogging game, and after having a quick browse, it appears widgets are extremely useful? I'm pretty naff on the computer, so if anyone could shoot me over some pointers, I would appreciate it!

You are right widgets are very useful.
They allow you to add all kinds of different content to your site.
Themes have different widget areas that allow you to put any of the available widgets on your pages / posts. A good starting point would be http://en.support.wordpress.com/widgets/

Then just go in and start adding some widgets and seeing what they can do.